Nowadays it is possible to use as a water purification device described above, that may easily be applied for most heterogenous circumstances, such as a minor housekeeping use or for especially demanding or difficult circumstances, an active carbon filter, that can be placed at the end of a supply pipe or on top of a jug. The above type of filters, usually intended for purifying drinking water, have lately become remarkably common particularly because of the increasing amount of allergies and pollution of environment. Water produced by the water distribution system, which as such satisfies the requirements of law, contains materials, such as carbonate and chlorine, which have not been known to have any influence on health, but which influence on the taste of water. It is possible to eliminate this kind of materials effectively particularly with the kind of active carbon filters described above. In addition to this with such filters it is also possible to reduce heavy metals, such as lead and possibly bacteria to some extent.
This kind of an active carbon filter, when applied in connection with a jug, is used for example so, that in the beginning it is kept immersed in water for a certain length of time, for example 15 minutes. Then the filter is placed on top of the jug, where-after the upper part of a hopper existing in the filter is filled with water, that may flow by itself through the filter into the jug underneath of the same. The filter must be kept in connection with the jug in such a way, that it remains continuously wet. In case the filter gets dry, the above treatment for a new filter must be repeated.
The types of filters described above reduce very effectively chlorine and organic compounds, that have an influence on the taste and the smell of water. However, the filters in question are not able to eliminate reliably enough a general problem concerning particularly demanding circumstances, that is bacteria from water intended for drinking. In respect with bacteria the type of filters have also such a problem involved, that the active carbon inside the filter in principle acts as a good substrate for the bacteria. This is why usually small silver flakes have been used in the filtering substance in addition to the active carbon to prevent bacteria reformulation.
Another notable problem related to the use of active carbon filters is that, controlling of the functional efficiency of the filter is impossible. That is why the filter must be replaced as a whole with a new one after a period of usage determined by guideline values. The reason for this is, that the filtering capacity of the active carbon filter depends both on the quality of the water to be used and on the amount of water led through it. As a general guideline, the filtering amount of water with this kind of active carbon filters is usually defined to be 60-100 liters and the exchange period is 3-4 weeks, whereafter the active carbon filter is unusable and must be replaced.
With active carbon filters of corresponding type, that may be placed at the end of a supply pipe, another problem is involved in addition to the one above, that is caused by pressure of the water distribution system. Usually the pressure in a water distribution system is very high, so that certain constructions must be applied in such filters used at the end of the supply pipe whereby water passes slowly enough through the filter to make possible a concrete result with the filtration.
Generally, the functional reliability and safety of the type of disposable active carbon filters described above are insufficient for certain purposes particularly because of the inadequate bacteria separation ability. Furthermore the functional capacity, that may not be controlled in any way, may decrease in certain circumstances very rapidly, whereby they may even make the quality of water worse, because of the bacteria formulation taking place in the filter.
On the one hand so called ceramic filters are known to be used as filters, also, that are intended for stationary placement in connection with supply pipes correspondingly as above. This kind of solutions is not particularly suitable for housekeeping purposes, because of the relatively big size and the high price of the same, nor to be used in primitive circumstances, either, because of the modern fitting procedures with standardized constructions. On the other hand there are nowadays on the markets certain types of manually or by syphon principle operating water purifiers equipped with ceramic filter parts.
This kind of a purifier includes a filter made of porous ceramic tube, that is immersed into unclean water. Water, that is purified while passing through the filter, is led with a flexible output pipe away from the unclean water container from above into for example, a suitable collecting container. The manual purifier includes a pressure cylinder equipped with a driving handle, wherein by pumping of the same a large enough negative pressure is affected inside the ceramic tube, by influence of which the above process starts and continues until the pumping is interrupted. A purifier functioning by syphon principle enables a self operated and a continuous purification by utilizing the syphon pressure caused by the height difference between the water container and the collecting place.
The purifiers described herein are heavy and large because of the use of the ceramic filter and furthermore they do not fulfill the requirements concerning difficult circumstances as far as manufacturing costs and functional reliability are concerned. Utilizing syphon principle in connection with a ceramic filter is also not particularly profitable, which is due to the high pressure drop, that is typical for a ceramic filter. Because of the high resistance of flow, the output of this type of a purifier is usually about 1 l/h, which requires furthermore usually a height difference of about at least 2 m. The increase of the output capacity requires thus the increase of the height difference or use of several parallel purifiers at the same time. Furthermore particularly the use of a manual purifier requires rather uncomfortable activities in the sense of ergonometry to keep the purification process going on.
Thus nowadays there are no water purifiers on the markets, that would suit to most heterogenous circumstances, be profitable by the acquisition or functional costs, be technically easy to utilize, operate effectively enough, and eliminate particularly bacteria in all kinds of circumstances reliably enough.